A tension exists between the diverse goals of minimizing size and weight of a wireless telephone (also called cell phones, mobile stations or mobile telephones) and the amount of time that the wireless telephone may be used without recharging the battery. Generally, the greater the battery capacity, the larger and heavier the battery is. While many advances have been made in battery technology to address this issue, efforts are being made in other areas of wireless telephone technology to conserve battery energy and hence lengthen the useful time of the wireless telephone between recharging.
In direct spread spectrum, code division multiple access (CDMA) wireless technology, there is recognition of a need for battery energy conservation. To this end, the IS95 CDMA standard specifies a "sleep mode" for the wireless telephone, wherein the components that consume the most power are turned off. When the wireless telephone is idle (that is, not on call and not receiving instructions from the wireless system), the wireless telephone is only listening on the paging channel for instructions or a page from the wireless system. Paging messages for a particular wireless telephone can occur from once every 1.28 seconds to once every 163.84 seconds. The wireless telephone can thus turn off the power to many of its components during the other times. This technique provides a very powerful method by which a battery-operated wireless telephone can conserve battery energy when idle.
A problem arises, however, when the components of the wireless telephone come out of the sleep mode. As is known in the art, most wireless communication systems use a centralized time reference to maintain synchronization of modulation and demodulation. Every wireless telephone includes an oscillator as frequency reference and input to a master timer or local system time reference. This oscillator is, in many cases, a temperature-compensated crystal oscillator that maintains precise alignment of the wireless telephone's clock to the system's reference clock. It is desirable to disable (power off) the temperature-compensated crystal oscillator because it uses a relatively large amount of power when active. However, to begin modulating and demodulating signals again, the master timer (local time reference) must be resynchronized to the network time reference when the oscillator is turned back on. One method for resynchronization is to acquire the synchronization channel as in the wireless telephone power-up routine. Such synchronization may take most of the time of the sleep period. In the worst case, acquisition of the synchronization channel may take more power than the master timer requires if it remained powered-on during the sleep period.
This invention is directed to solving one or more of the above-described problems.